1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine and more particularly to such a system having a high pressure pump connected to a fuel injection valve for each cylinder of the engine.
The invention is based on a fuel injection system for an internal combustion engine as generically defined by the preamble to claim 1.
2. Description of the Prior Art
A fuel injection system known from EP 0 987 431 A2 has a high-pressure fuel pump that is connected to a fuel injection valve for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston that defines a pump working chamber and is driven into a stroke motion by the engine. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve element that controls at least one injection opening; the pressure prevailing in the pressure chamber can move the injection valve element in the opening direction counter to a closing force in order to open the at least one injection opening. A first electrically actuated control valve controls a connection of the pump working chamber to a relief chamber. A second electrically actuated control valve controls a connection of a control pressure chamber to a relief chamber. A control piston defines the control pressure chamber; the pressure prevailing in the control pressure chamber causes the control piston to act on the injection valve element in a closing direction and this control piston can move in concert with the injection valve element. The control pressure chamber has a connection to the pump working chamber. For a fuel injection, the first control valve is closed and the second control valve is opened so that high pressure cannot build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, though, fuel flows out of the pump working chamber via the control pressure chamber so that the fuel quantity available for the injection is reduced along with the fuel quantity supplied by the pump piston and the pressure available for the injection is reduced as well. It follows from this that the efficiency of the fuel injection system is not optimal.
A fuel injection system of this kind is known from EP 0 987 431 A2. This fuel injection system has a high-pressure fuel pump that is connected to a fuel injection valve for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston that defines a pump working chamber and is driven into a stroke motion by the engine. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve element that controls at least one injection opening; the pressure prevailing in the pressure chamber can move the injection valve element in the opening direction counter to a closing force in order to open the at least one injection opening. A first electrically actuated control valve is provided, which controls a connection of the pump working chamber to a relief chamber. A second electrically actuated control valve is also provided, which controls a connection of a control pressure chamber to a relief chamber. A control piston defines the control pressure chamber; the pressure prevailing in the control pressure chamber causes the control piston to act on the injection valve element in a closing direction and this control piston can move in concert with the injection valve element. The control pressure chamber has a connection to the pump working chamber. For a fuel injection, the first control valve is closed and the second control valve is opened so that high pressure cannot build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, though, fuel flows out of the pump working chamber via the control pressure chamber so that the fuel quantity available for the injection is reduced along with the fuel quantity supplied by the pump piston and the pressure available for the injection is reduced as well. It follows from this that the efficiency of the fuel injection system is not optimal.